There is an ongoing need for providing novel improved electrical storage batteries, which are low-cost and high energy density. The two most commonly used types of batteries are the lead-acid battery as employed in automobiles and the dry cell as used in most flashlights. The light weight of sulfur, makes sulfur-based batteries to be quite attractive for electrochemical energy storage and accordingly a variety of metal-molten sulfur batteries are described in the literature. High temperature molten alkali sulfide batteries have been investigated, but serious problems were encountered with the high temperatures required for maintaining a liquid phase, the electrical insulation, passivation of sulfur, as well as safety considerations.
Although less conductive than molten salts, the often toxic. oganosulfo cathodes, such as discussed in the U.S. Pat. No. 4,833,048, using materials of the general formula (R(S).sub.y).sub.n, where R is a chemical component containing from 1 to 20 carbon atoms, can be used as a cathode, however the additional weight of the carbon will decrease the electrical storage capacity. Recently, concentrated aqueous polysulfide solutions were found to provide a medium for highly reversible two electrons redox chemistry at ambient temperature. In a paper by the present Inventor (Journal Electrochemical Society, 1987, 134, p. 2137-41) aqueous sulfur redox cells were mentioned to possess a high faradaic capacity. The cells are utilizing electrolytes which by their mass could accommodate more reducible sulfur than water. In a later paper (Journal Electrochemical Society, 1993, 140, p. L4) the inventor describes aluminum-sulfur batteries based on concentrated polysulfide catholytes and an alkaline aluminum anode.
The present Inventor also described in his prior U.S. Pat. No. 4,828,942 an aqueous sulfur cathode containing at least 20% by weight sulfur in a battery with a sulfide anode. The room temperature sulfur electrolyte, provides a conductive and reversible battery which possesses a high capacity half-cell storage material. In 1993, the capacity of the cathode was further increased by the addition of solid sulfur, as described by Peramunage and Licht, (Science, 1993, 261, p. 1029). According to the recent U.S. Pat. No. 5,424,147 (by Khasin) a water-activated, deferred-action battery is disclosed. The cathode of the battery is made from a skeletal frame which comprises cuprous chloride, sulfur, carbon and a water-ionizable salt, compacted and fused under pressure and heat. The sulfur in the cathode acts to improve the discharge of the cuprous chloride, but the sulfur itself is not discharged. The anode is selected from the group consisting of zinc, magnesium, aluminum and alloys thereof. Although this type of battery has an advantage by not using lead, known by its environmental problem, it suffers from a disadvantage connected with the manufacture of the skeletal frame of said cathode. From a storage capacity and environmental view, zinc is an attractive anode material which is used in several batteries including dry cells. However, a zinc anode cannot be oxidized in an aqueous solution containing sulfur, because the product of the discharge is zinc sulfide: EQU Zn+S.sup.2-.fwdarw.ZnS+2e.sup.- (1)
The present Inventor determined than zinc sulfide was even less soluble than previously thought. (Journal Electrochemical Society, 1988, 135, p. 2971) which would prevent dissolution, with a solubility product of 10.sup.-25.4 given by: EQU ZnS.sub.solid,precipitate {character pullout}Zn.sup.2+ +S.sup.3- K.sub.sp =10.sup.-25.4 =[Zn.sup.2+ ][S.sup.2- ] (2)
This zinc sulfide is a highly insoluble salt and creates a layer which passivates zinc and rendering it completely ineffective to battery discharge.
It is an object of the present invention to provide a safe and reliable battery, capable of producing high energy densities. It is another objective of the invention is to provide a battery made of relatively inexpensive materials.